Electric impulse receiving and timing arrangement



Sept. 30, 1947. G. c. HARTLEY ETAL 7 2,428,023

ELECTRIC IMPULSE RECEIVING AND TIMING ARRANGEMENT Filed Oct. 15, 1943 v 2 Shets-Sheet 1 boooeooooobo Sept. 30, 194% eflc. HARTLEY ET AL 2,

ELECTRIC IMPULSE RECEIVING AND TIMING ARRANGEMENT v Filed Oct. 15, 1945 2 Sheets -Sheet2 NUMBER I I I I Patented Sept. 30, 1947 ELECTRIC IMPULSE RECEIVING AND TIMING ARRANGEMENT George Clifl'ord Hartley and William John Reynolds, London,

England,

assignors to Standard Telephones and Cables Limited, London, England, a British company Application October 15, 1943, Serial No. 506,322 In Great Britain December 15, 1942 Section 1, Public Law 690, August 8, 1946. Patent expires December 15, 1962 12 Claims. 1

This invention relates to an arrangement for receiving and regenerating electric impulses and has for its object to provide a circuit arrangement by means of which signals consisting of impulses of uncertain duration and divided into trains of impulses with a minimum interval between such trains may correctly operate apparatus for registering such impulses.

According to one feature of the invention an arrangement for receivin and regenerating electric impulses comprises an impulse responding relay, a second relay the response of which is dependent upon the impulse responding relay and is timed by means of a condenser connected in its circuit and means for maintaining said impulse responding relay in the condition caused by a received impulse until the completion of response of said second relay.

According to a further feature of the invention an arrangement for receiving electric impulses and for timing a pause between trains of impulses comprises a relay the response of which is dependent upon the impulse responding relay and is timed for release and re-energisation in a selfinterrupting circuit by means of a, condenser connected in its circuit, means for releasing said relay for self-interruption during a pause between trains of impulses, and means controlled by the release and re-operation of said relay to time said pause and discriminate between such pause and the cessation of impulsing.

The invention will be better understood from the following description of one embodiment thereof taken in conjunction with the accompanying drawings in which Fig. 1 and Fig. 2 are two alternative circuits for a substation in an electric signalling system.

Referring to the drawings and first more particularly to Fig. 1, signals from a transmitter will be received by a plurality of substations each arranged after the manner shown in the drawing, each substation being connected over a line L to a common circuit. This circuit may be a party line or it may be that the messages are sent by radio to a plurality of stations each tuned to the same frequency. The impulses consist of interruptions of an alternatin current which is rectified and applied to the control electrode of a three electrode gas-filled tube T. The arrangement is such that normally no alternating current is being received. The receipt of alternating current indicates that a message is about to be sent and the received alternating current when rectified fires the tube T and operates the relay C. The circuit is then automatically changed so that the discharge in the tube T is extinguished and subsequently a cessation of alternating current constituting an impulse causes a, discharge in the tube T. Received impulses will step the selector switch SR shown which is stepped by a magnet SRM and has five wipers and five banks of contacts. The first three trains of impulses constitute a station selecting code and the total number of impulses in these three trains is a constant total of 11. Subsequent trains of impulses cause the selector switch to be stepped two steps for each successive train of impulses. At the station for which the message is intended the successive trains of impulses are routed to the wires NIA-NIF. To each of these wires is connected a number indicator of the kind in which a rotating selector switch or other device is stepped by i a sequence of impulses. The magnets 01- all the indicators are connected to a common terminal H to which ground is applied from the circuit shown in the drawing when it is desired to operate the indicator and to keep it operated. If the correct station code is not received, the selector switch will be stepped as stated above, but the trains of impulses are not routed to the wires NIA-NIF. Any message set up on the number indicators remains until the station code is again received, when it is cancelled and a further message set up.

The operation of the circuit shown will now be described in detail. The line L is connected to the primary of a transformer TR, the secondary of which is tuned to the desired frequency. In the drawing all relays except ED are shown in their unoperated condition. In the normal condition of the circuit it will be observed that there is a circuit for the relay ED from ground over back contacts ssl, lower winding of relay ED, home contact and wiper of bank I of the switch, switch magnet SRM and negative battery. The current in this circuit is insufficient to operate the magnet SRM, but the relay ED is operated therein. Contacts edl prepare a circuit for relay C. When alternating current is received over the transformer TR it is rectified by the rectifier RA and applied over back contacts 82 and resistances R2 to the control electrode of a tube T and assists a positive potential of 40 volts connected to the back contacts 81. This tube is a cold cathode gas-filled tube having three electrodes to one of which (the anode) a potential of approximately 150 v.+ is applied. The other two electrodes are similar and either of them functions as the cathode or the control electrode. The electrode to which the rectified alternating current is applied will be hereafter called the control electrode and the other the cathode. Normally the cathode is connected over contacts 83 back, ed! front, winding of relay C to ground, and when rectified alternating current is applied to the control electrode a discharge is initiated in the tube T, current flows through the winding of relay C and that relay operates. At front contacts cl, a circuit is closed for'relay P (negative, winding of P, ed2 front, ss2 back, cl front, ground) which operates. its lower winding to contacts pl front and ground, and at contacts s4 front closes a circuit to operate relay SS over 54 front, pl front and ground. Contacts '83 open and remove potential from the cathode of tube 'T whereupon the discharge in the tube T is extinguished and relay C releases. At contacts sl and s2 the potential of 40 v. previouslyapplied to the control electrode of tube T is removed and potential of 80 v. is applied in opposition to the received rectified current from contacts s2, resistance Rl, front contacts sl. At contacts cl the original operating circuit for relay P is opened but this relay looks over p2 front and cl back. When relay P was first operated it closed a circuit for relay Y at contacts 103 front and it operates. When relay C releases a circuit is closed for relay X over '02 back and ssi front and it operates. At contacts all front, relay G is operated and at contacts gl closes a circuit which holds relays S and SS operated independently of relay P. The operating circuit for relay ED is opened at contacts ssl and this relay releases. An alternative energising circuit for relay C is prepared at front contacts $36 and front contact g2. At contacts ss5 ground is applied to a wire BL to indicate that current is being received.

When impulsing commences the impulses take the form of brief interruptions of the alternating current and when the alternating current ceases the potential of 80 v, applied to the control electrode of tube '1 is sufficient to initiate a discharge in the tube and operate relay C. The discharge once initiated remains, and relay C remains operated, even when the impulse comes to an end. A circuit for magnet SRM is closed over front contacts cl, front contact ss2, back contacts 2|, magnet SRM and battery, and this magnet energises. At contacts cl the circuit of relay P is broken and that relay releases. At contacts 02 the circuit for relay X is broken. This relay is maintained energised because of the condenser connected to-its second winding for approximately 40 ms. before it releases. When relay X has released contacts .102 connect a condenser CA (which ha been discharged to ground through contact x2front) to'the anode of tube T and cause the potential of the anode to "be thus reduced sufliciently to extinguish the discharge in tube T, provided that the incoming impulse has ceased and alternating current is once more being received. Relay C releases and contacts cl break Relay S operates over 4 the circuit of the magnet SRM which thereupon steps it wiper to the next set of contacts. Contacts c2 reclose the circuit for relay X which reoperates after a further 40 ms. It will be seen that the impulses which are received are regenerated and the length of the impulses applied to the magnet SRM is independent of the length of the incoming impulses and depends mainly on the release time of relay X.

In the embodiment described the release of relay X brings the impulse to an end but it will be understood that relay X, could be normally deenergised,'its circuit closed on the receipt of an impulse and serve by this operation instead of by its release to bring the regenerated impulse to an end.

The above described changes take place at each received impulse, the switch SR stepping its brushes each time. Relay Y is kept operated during impulsing either over 02 front and ssl front, or over ss3 front and as! back. At the end of a digit one interruption of incoming current i omitted as an interdigital signal. When relay X has reoperated after the previous interruption, if the tube T is not again ignited, and relay C again operated, the circuits for relay Y are interrupted and relay Y releases after about 40 milliseconds. Its circuit is immediately reclosed over yl back, eci3 back. RelayY will re-operate again after about another 40 milliseconds.

A single release and re-operation of relay Y serves to indicate an interdigital pause. During the period of relay Y back a test is made as to whether the code is for the station shown. Contacts No. I to Iii in bank 3 of the selector switch are connectable by removable links to relay W, certain of these links being omitted in accordance with the station code. The code of the station shown is 452 and the links for contacts Nos. 4 and 9 (4+5) are'removed. If the selector switch has,' after the first train of impulses come to rest on any other contact than No. 4, a circuit is completed, whilst relay Y is back, from ground, cl back, 122 back, 112 back, ss4 front, wiper and contact of bank 3 of the switch, relay W, battery. Relay W operates and closes a, locking circuit for itself over wl front to Q! front and ground. Operation of relay W prevents any mes sage being transmitted to the number indicators as will be clear from the description hereinafter.

The second and third trains of impulses are received in the same'manner as the first and the magnet SRM operated and released to step the wipers of the switch in the same manner as before. During the second interdigital pause, a circuit for relay W is again completed and if relay W has not previously operated and the switch has come to rest on a contact other than No. 9, relay W will be operated this time. If, however, the selector switch shown comes to rest on contact No. 4 after the first train of impulses and on contact No. 9 after the second train of impulses, relay W remains unoperated.

If a correct code be received, a total of eleven impulses will be received in three trains of impulses and the selector switch wipers will come to rest on contact No. .l I. When Y releases during the interdigital pause following, a circuit is completed for relay Z, from ground, cl back, 502 back, 112 back, cs4 front, contact No. 11 in No. 3 bank, rectifier MRA, 2a! back, winding of Z, negative battery. Relay Z operates and looks over 22 front, rectifier MRB, gl front, ground.

At contacts zi relay Z disconnects magnet SRM from the original impulsing circuit and connects relay AX in its place. At contacts 23 a circuit is completed for a calling lamp to wire CL. After the station identification code, a digit 0, represented by some predetermined number of impulses, is sent. Relay AX responds to the impulses, in a circuit over zI front, cs2 front, cI

front. On the first operation of relay AX, relay ZA operates over contact No. II of bank 5 of switch SR, aarI front, ground, and locks over 2112 front, rectifier MRB, gI front, ground. Other operations of AX have no effect at this time.

When the interpolated digit ends, relay Y releases during the interdigital pause and a circuit is completed for relay ZB over zaI front, rectifier MRA, contact I I of bank 3 of switch SR and wiper 3, ss4 front, 112 back, 112 back, cI back. ZB operates and locks over zbI front, a l front. A circuit is completed for magnet 'SRM over za4 front, contact and. wiper of bank 4 of switch SR, 884 front, g2 back, p2 back, cI back, and when Y re-operates, magnet SRM steps the wipers of the switch on to contacts No. I2.

When the next digit is received relay AX responds to the impulses, contacts (1:82 repeat the impulses over 2122 front and 1122 back, contact I2 of bank 2 to wire NIA and to a number indicator. A circuit for holding all the number indicators is completed over w3 back, zb3 front to wire H. It will be seen that if relay W had previously operated, th'ese circuits would not be completed and thus no message impulses are recorded at a station for which they are not intended.

On the first operation of relay AX, contacts aml complete a circuit over contact No. I? of bank 5 for magnet SRM and when relay AX de-energises, the wipers step to contact I3. Impulses continue to be sent to wire NIA over contact I3 of bank 2.

At the end of the digit, relay Y releases during the interdigital pause and magnet SRM again operates over contact 13 of bank 4, wiper No. 4, 884 front, 112 back, 102 back, cl back, and when Y re-operates, magnet SRM releases and steps its wipers on to contact I4.

The following digits of the message are distributed to wires NIB, NIC, NID, NIE. and NIF, to which number indicators are connected in the same way, all the number indicators being held by ground connected to wire H. On the last digit of the message, the wipers of switch SR step on to contacts No. 23 on the first impulse and when Y releases and re-operates after the end of impulsing step on to contacts Nos. 24.

The message ends after the last digit with tone which persists for the same period as an interdigital pause, but then ceases. This causes a discharge in tube T and relay C operates. Relay AX operates to front contacts cI and at contacts azrI operates relay F over contact No. 24 of bank 5. Relay F locks over front contacts f2, front contacts 2124, back contacts e114.

Relay X releases after an interval, but its contacts x2 do not extinguish the discharge in the tube T since there is now no tone to oppose the bias applied to the control electrode. After an interval relay G releases, since its circuit is broken at contacts :cl. At contacts oi, the circuits of relays S, SS (W if operated), Z and ZA are broken. Contacts 24 in changing over break the circuit of relay ZB, but hold relay F operated when contacts 2224 open. At contacts f3 th number indicators are held to display the message received by maintaining ground on wire 1-1.

When relay S releases its contacts sI and s2 remove the bias from the control electrode of tube T and contacts g2 disconnect relay C from the cathode and thus also remove the earth potential therefrom, and thus discharge in tube T is extinguished. Relay C releases.

Relay AX releases and contacts 583 open the circuit of relay Y. Relay Y releases after an interval and completes a circuit for magnet SRM over wiper and commoned contacts of bank I, 884 back, 1 2 back, 112 back, cl back. When relay Y reoperates its circuit being closed over yl back, ed3 back, the wipers of switch SR step on to the home contact. Relay ED operates over ssI back, lower winding of relay ED, home contact and wiper of bank I, winding of stepping magnet SRM.

The circuit remains in this condition, with the last message received displayed upon the number indicator until current is again received over transformer TR. The changes previously described then take place. When impulses commence, the selector switch is stepped, as previously described. If the code signal first received be that for the station shown, relay Z operates as previously described and at contacts a l, breaks the holding circuit for relay F, and over contacts ,*I back, .23 front the calling lamp CL is lit and at contacts f3 the holding circuit of the indicators is broken and they return to normal. The interpolated digit referred to above is of long enough duration to ensure this return to normal.

Should however a code for some other station be received, relay W operates, as previously described, and at contacts w3 maintains relay F operated. Thus the previous message received remains displayed until the code of the station shown be received, indicating that a further message is about to be received.

It will be clear from the above that the release and i e-operation of Y takes place in an interdigital pause. Thus if an impulse fails to be properly received, this will be interpreted as an interdigital pause and the received code will appear to contain an additional train of impulses. If this takes place during the first part of the received code, i. e. the part selective of the station to receive the message, the selector switch will not receive the correct total number of impulses and there will be no operation of relay Z. Relay W will be operated and the code message will not be displayed. If an impulse is missing in the message part of the code and thus an additional digit be received, the operation is as follows:

At the end of the sixth digit, the wipers of SR are stepped from contact 23 to contact 24. If new relay AX responds to a further received impulse, relay F is operated from aarl front over contact 24 of bank 5, and locks over 2 front. At the end of this extradigit relay Y releases and completes a circuit for magnet SRM, contact 24 of bank 4, wiper 4, s34 front, 212 back, 192 back, 0! back, and when Y re-operates, SRM steps the wipers on to the home contact. At the end of the impulsing, relay AX responds as previously described, and contacts axl complete a circuit over bank 5 for relay ED. At contacts ed l, the holding circuit for relay F is broken and when the circuit returns to normal the indicator will also return to normal.

Relay Y provides a safeguard against an interdigital pause that is too long. For each digit of the message the switch SR takes two steps, and on the release and reoperation of Y during an interdigital pause the wipers are stepped on to a contact connected to a different number indicator.

Thus the first digit of the message is received on contacts 12 and I3 and in the interdigital pause the switch is stepped to contact ls. If now relay Y releases a second time whilst the switch is on this contact, relay W operates over bank 4, ss i front, g2 back, p2 back, cl back and locks. Contacts 203 remove holding potential from the number indicators at wire H, which re, lease if the message were intended for the station shown. Otherwise relay F remains operated to hold the indicator.

If the message is a digit short, release will not occur when the wipers are on contacts 24 and thus relay F will not be operated and the indicators will release when relay ZB releases.

A message may be broadcast to all stations by sending eleven impulses. This will cause the wipers to step to contacts H and relay Z will operate independently of the receipt of the individual code of the station shown. When relay Z is operated the indicator is released. Thus if the code of the station on the eleven impulses be received and impulsing then ceases without any message being sent the set up message is cancelled and the selector switch stepped to its home position over bank I, by impulses from contacts 1112.

Referring now to Fig. 2, this shows a somewhat simplified and improved version of the circuit of Fig. l. The gas filled tube T has been replaced by a thermionic valve Ti and the impulse receiving relay C by an impulse receiving relay A. As in Fig. 1 when the circuit is seized by the receipt of alternating current relay A operates, but thereafter the receipt of impulses is denoted by the release of relay A.

When relay A operates, contacts a2 close the circuit of relay AX which operates. Contacts a! close in order to keep the grid circuit of valve Ti closed when relay X operates. Contacts (13 close a circuit for relay X which operates after about 40 ms. Contacts x! close a circuit for relay G which operates. Relay G is slow releasing and remains operated throughout subsequent release periods of relay ,X. Contacts mZ open a path in the grid circuit of the valve Tl parallel to that closed by contacts at. Contacts g'l prepare a circuit for switch magnet SRM'. Contacts 9'3 prepare a circuit for relay W. Contacts 9'4 close a circuit to wire BL to light a busy lamp. Contacts y'2 complete a circuit for relay Y, over g2 front, 1! back, home contact and wipe-r of bank 5 of the selector switch SR, to positive.

Impulses consist of interruptions of alternating current and on such an interruption relay A releases. At its contacts a! it opens the grid circuit of the valve Ti, so that even if the received impulse is short, relay A cannot re-operate until relay X has released. At contacts a2 a. circuit is completed for switch magnet SRM' (negative, SRM, 9! front, w4 back, 2''! back, a2 back, positive), which operates. At contacts 113 the circuit of relay X is broken, but this relay does not close its back contacts until after about 40 milliseconds.

When relay X has released and alternating current is again received over the line L, relay A re-operates and at contacts a2 breaks the circuit of magnet SRM which releases and steps the wipers of the selector switch. The selector switch is thus stepped in response to the impulses. Relay Y remains operated during a train of im- 8 pulses, its circuit being completed over 9'2 front and either a3 back or :c'l back.

As in the case of the circuit of Fig. 1 relay Y has time to release during an interdigital pause and relay W is able to operate if the wiper 4 of the selector switch has come to rest on a contact other than that denoting the station code (negative, relay W, contact, wiper of bank 4, yi back,

. a:1:2 front, positive), and locks over w3 front, g'3

front, and positive. Relay W at contacts w4 opens the circuit of magnet SRM and further impulses will have no effect.

If the station code has been correctly received, the wipers reach contacts No. II, relay Y releases on the interdigital pause, and relay Z operates (negative, relay Z, k3 back, contact No. H and wiper of bank 4, 3 back, a:r'2 front, positive). Relay Z looks over 2'6 front, to 9'3 front and positive, and at contacts a! connects positive to wire CL to light a calling lamp. At contact 2'2 a resistance in series with the holding magnets of the call indicator (connected to wire H) is short circuited. At 2'3 a circuit is prepared for the impulses to go to the number indicators. Contacts z'l change over the impulsing circuit so that magnet SRM is no longer operated on each impulse. On the first impulse of the next series of impulses a circuit is completed for relay H (negative, lower winding of relay H, contact No. I! and wiper of bank No. 3, 2'5 front, arZ back, positive). The circuit for the holding magnets of the number indicator is broken by hi and any existing message displayed thereon is cleared. Relay H remains operated in a circuit over its upper winding, wiper and contact No. II of bank No. 2, hi, positive.

When relay Y releases at the end of the series of impulses, a circuit is completed for magnet SRM over gl front, w l back, a? front, k3 front, contact No. II and wiper of bank 4, y! back, amZ front, positive. When relay Y re-operates this circuit is broken and the wipers of the switch step to contact No. i2, whereupon relay H releases and recloses at contacts hi the circuit for the holding magnets of the number indicator.

When the first impulse of the next set of impulses is received it is repeated by contacts as! over w2 back, 2'3 front, wiper and contact of bank I to wire NIA. A circuit is completed from magnet SRM', over gl front, wfl back, 2''! front, contact No. i2 and wiper of bank 3, 2'5 front, am2 back, positive. After the first impulse magnet SRM de-energises and the wipers step to contact No. l3. Over this contact of bank i the impulses continue to go to the wire NIA.

At the end of the digit, relay Y releases and closes a further circuit for magnet SRM over wiper and contact No. I3 of bank 4 and when relay Y operates again, the wipers step to contacts Nos. I l. As before succeeding digits are sent to the wires leading to the number indicator over pairs of contacts, the last digit being sent over contacts Nos. 22 and 23 of bank I. When relay Y releases at the end of this last digit, magnet SRM is energised as before, but relays A and AX remain operated. There is, however, a circuit to re-operate relay Y over yZ back, r2 back, contact No. 23 and wiper of bank 5, positive. Relay Y re-operates, whereupon magnet SRM is de-energised and the wipers step to contacts Nos. 24.

The signalling now comes to an end and the alternating current ceases before relay Y has time to release again so that relays A and AX release. When relay AX releases a circuit is closed for relay R over hZ back, contact No. 24 and lay,

wiper of bank 3 of the switch, 2'5 front, axZ back, to positive. After aninterval relay G releases, and relay Y also releases, but a circuit exists for relay Y over y2 back, contact No. 24 and Wiper of bank to positive, and after an interval relay Y re-operates. There is then a circuit to operate magnet SRM over g I back, 2/2 front and the same circuit as for relay Y. After an interval relay Y again releases and magnet SRM steps its wipers to the home contact. Relay R releases and rela Y also releases after an interval and the circuit returns to normal.

If the station code were not received and relay W has been operated, the switch remains on contact No. l l until impulsing ceases and until relay G has released at the end of the message. When relay Y releases a circuit exists for it over'its own back contacts yZ and contacts Nos. H to 22 of bank 5, so that relay Y re-operates and operates magnet SRM over gl back, 112 front. Relay Y continues to release and re-operate, operating and releasing magnet SRM' to step the wipers to contacts Nos. 23. In this position magnet SRM operates over 9'! back y2 front, r2 back, contact No. 23 and wiper of bank and when relay Y releases, the wipers step to contacts Nos. 24. Whilst the wipers are on contacts Nos. [2 to- 23 the locking circuit of relay H is maintained over its upper winding, contacts and wiper of bank 2, 2'5 back, hi front, positive. On contact No. 24 the locking circuit of relay H is maintained independently of contacts 2' 3. The wipers step from contacts Nos. 2% to the home contacts in the manner described above, where relay H still remains locked in a circuit over the wiper and contact of bank No. 2 but again including back contact z l.

What is claimed is:

1. Apparatus for receiving and regenerating electric impulses comprising an impulse responding relay, a second relay, means tocause the response of said second relay to be dependent upon said impulse responding second relay including means to time the operation thereof, and means for maintaining said impulse responding relay in the condition caused by a received impulse until the completion of response of said second relay.

2. Apparatus as claimed in claim 1 and an electrical discharge device (for controlling the operation of said impulse responding relay, and a circuit for controlling said discharge device controlled by the second relay.

3. Apparatus as claimed in claim 1, a normally inactive electrical discharge device for controlling the operation of said impulse responding rea circuit for operating said device by the impulses, and a circuit controlled by the second relay for maintaining said device operated.

4. Apparatus as claimed in claim 1, a normally inactive electrical gas discharge device having an anode, a cathode and a control electrode, an energizing circuit for said impulse responding relay connected to said cathode, a circuit for applying the impulses to the control electrode, and a circuit for the anode controlled by the second relay.

5. Apparatus as claimed in claim 1, a normally inactive electrical discharge tube having an anode a grid and a cathode, a circuit connecting the anode to said impulse responding relay, a circuit for applying the impulses to the grid, and a circuit for controlling the cathode controlled by the second relay.

relay, a circuit for said 6. Apparatus for receiving electric impulses and for timing a pause between trains of impulses comprising an impulse relay, a second relay, means to cause the response of said second relay to be dependent upon said impulse responding relay, a self-interrupting circuit for said second relay for timing the release and re-energisation olf saidlsecond-relay, means for releasing said second relay for self-interruption during a pause between trains of impulses, and means. controlled 'by the release and re-operation of said relay to time said pause and discriminate between said pause and the cessation of impulsing.

'7. Apparatus for receiving and regenerating electric impulses comprising an impulse responding relay, a second relay, means to cause the response of said second relay to be dependent upon said impulse responding relay, a circuit for'said second relay including means to time the operation thereof, means for maintaining said impulse responding relay in the condition caused by a received impulse until the completion of response of said second relay, a selector switch, and means for causing the impulse responding relay to repeat the received impulses to said selector switch.

8. Apparatus as claimed in claim '7 in which a plurality of display devices are provided, means is provided to step said selector in response to the impulses repeated, and means responsive to impulses following a predetermined sequence of impulses to step said selector to connect said display devices for successive operation in accordance with, the repeated impulses.

9. Apparatus as claimed in claim '7 in which a plurality of display devices are provided, means to step said selector switch in response to impulses means responsive to impulses following a predetermined sequence of impulsesto step said selector successively to connect said display devices for operation in accordance with the re peated impulses, and means to hold said display devices actuated until said predetermined se quence of impulses is again received.

10. Apparatus as claimed in claim 7 in which a plurality of display devices are provided, means to step said selector switch in response to 11m pulses, means responsive to impulses following three successivetrains of impulses to step said selector to connect said display devices for successive operation in accordance with the repeated impulses.

11. Apparatus as claimed in claim '7 in which a plurality of display devices are provided, means to step said selector switch in response to impulses, means operative after the receipt of a plurality of trains of impulses to step said selector two steps for each impulse repeater successively to connect the display devices for operation in accordance with additional impulses received, means to hold said display devices actuated until said plurality of trains of impulses is again received, and means operative thereupon for releasing said display devices.

12. Apparatus for receiving and regenerating electric impulses comprising a line, a plurality of stations connected therewith, at each station a discharge tube having one electrode connected with said line to cause said tube to respond to impulses received on said line, an impulse responding relay connected to another electrode, a second relay, an energizing circuit for said second relay controlled by said impulse responding relay, means to time the operation of the second relay, means for maintaining said impulse re- V V 2,42s,o2s 11 12 spending relay in the condition caused by a 'received impulse until the completion of response "REFERENCES CITED of said second relay, a selector switch, a display The following references are of record in the device, means for repeating the received imfil of t i patent:

pulses, means for operating said selector switch "5 r I in accordance with some of the repeated im- UNITED STATES PATENTS pulses for selecting one of said stations, and Number Name Date means responsive to additional impulses for op- 2,091,551 Low Aug. 31, 1937 erating the selector switch to connect the dis- A- 2,315,705 Holden Apr. 6, 1943 play device for operation by further repeated 10 2,332,912 Hecht -Oct 26, 1943 impulses. 2,338,642 Holden Jan. 4, 1944 GEORGE CLIFFORD HARTLEY. 2,071,072 Johnson Feb. 16, 1937 WILLIAM JOHN REYNOLDS 2,071,078 Low Feb. 16, 1937 

